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Anything wrapped in {{ }} inside a workflow string (like task_template) is a template variable. You do not invent their values at write time — Cadence fills them at dispatch. This page is the complete contract.

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Resolution order (exactly four steps)

When Cadence renders a template string it resolves each {{name}} in this order — first match wins:
PrioritySourceExamplesWho provides the value
1Fixed slots{{workflow_id}}, {{issue_ref}}, {{ticket.id}}Cadence, always. Never you.
2Declared arguments{{topic}}, {{experts}}The caller at dispatch; coerced to your declared type
3Dispatch payload lookup{{project_id}}, {{reason}}, {{input.<field>}}, any {{path.to.value}}The ticket/event that triggered the run
4Unresolved—Renders as empty string — declare an argument with a default if that’s not acceptable
Variable names match [a-zA-Z0-9_.-]+. Scalar fields also support an inline fallback: {{model | default: 'claude-opus-4-7'}}.

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The fixed slots, demystified

{{workflow_id}} — the id: from your own frontmatter (e.g. my-first-workflow). Format: the kebab-case string you wrote. You “get” it by writing it; Cadence echoes it back so the agent always knows which policy file governs it. {{issue_ref}} — the reference of the ticket/issue that triggered this run (e.g. a Beam issue like BEAM-42). Comes from the dispatch event; empty when a run isn’t ticket-driven. {{ticket.id}} — the underlying ticket identifier from the dispatch payload. Where they go afterwards (analytics): these same values are stamped on every harness event in the session ledger (run ids, workflow id, lane slug, usage, cost). That means the {{workflow_id}} you chose is your join key across runs, costs, and evidence — pick meaningful ids.

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Declaring your own variables

Add typed arguments at the top level; callers supply values at dispatch, Cadence coerces and validates: 
arguments:
  topic:
    type: string
    required: true
  experts:
    type: int
    default: 3
agent:
  task_template: "Research {{topic}} with {{experts}} experts for {{issue_ref}}."
Types: string, int, number/float, bool/boolean. A missing required argument fails dispatch loudly — it will never silently render as empty. A declared argument always beats a same-named payload field.

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Rules of thumb

WantDo
Pass a user choice into the promptDeclare it in arguments (typed, defaulted)
Reference the triggering ticketUse {{issue_ref}} / {{ticket.id}} — never hardcode
Survive missing payload fields{{field | default: 'fallback'}} or an argument default
Trace a run in the ledgerFilter by your workflow_id

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See also